This laboratory study tests the hypothesis that left ventricular function following mitral valve replacement may be better preserved by retaining the tethering effect of the mitral valve apparatus in chronic mitral regurgitation. The specific aims are as follows: we will develop a chronic animal model of mitral regurgitation which allows the repeated measurement of left ventricular systolic and diastolic dimensions and mechanisms, regurgitant and forward flow across the valve (directly and via Doppler ultrasound), myocardial oxygen consumption, and hemodynamics. The effect of the acute loss of all the mitral valve attachments versus loss of the anteriod leaflet attachments versus preservation of all structures on left ventricular mechanics, dimensions, and metabolism will be determined. The utilization of a specifically designed left atrial flow transducer allows direct measurement of regurgitant flow thus permitting further validation of color Doppler mapping - a technique being investigated in this laboratory.